PS 36-184 - CANCELLED - Greater leaf succulence and lower root allocation is related with drought avoidance in succulent subshrubs and shrubs

Background/Question/Methods

Leaf succulence describes plant water storage in cells or organs, regardless of plant life-form and exists not only in true succulents. Greater leaf succulence means a larger internal water availability and may improve drought survival. Studies have shown that plants which resist drought generally have increased root allocation; however, it is unclear whether there is a trade-off between leaf succulence and root allocation. It is also unclear how leaf succulence and root allocation relate to plant drought resistance strategies, including avoidance (increased water uptake/decreased transpiration to maintain water status), tolerance (adjusting cell turgor to tolerate low water status) and escape (finishing life cycle before drought).

To evaluate how leaf succulence and root allocation relate with plant drought resistance strategies, we selected 12 Australian species of subshrubs/shrubs with differing leaf succulence from two families (Aizoaceae and Amaranthaceae) and conducted a glasshouse dry-down experiment in 10.5 L pots. Plant drought response measures included hydroscape area, plant water use, turgor loss point and predawn water potential when transpiration ceased. Principal component and cluster analyses were used to evaluate variation in morphological traits and measures of drought response; and to determine possible functional groups. Pearson correlation was used to test relationships among individual traits.

Results/Conclusions

We observed a trade-off between root allocation and leaf succulence in these 12 subshrub/shrubs. Greater leaf succulence and lower root allocation were associated with drought avoidance strategies. These drought avoiders ceased transpiration at less negative predawn water potential (Ψ_PD) and had smaller hydroscape areas. All 12 species had very high turgor loss points (Ψ_TLP; -1.32 MPa to -0.59 MPa) and the Ψ_TLP did not correlate with Ψ_PD when transpiration ceased or hydroscape area. These results suggest that woody plants with high leaf succulence do not utilise this stored water to maintain transpiration in drying soils. Instead, early stomatal closure means that high succulence is used to maintain plant water status and ensure survival during drought. This also highlights why there is a trade-off between leaf succulence and root allocation, as plants with high leaf succulence likely will not access water in deeper soil layers.